Investigators will prospectively include 40 postmenopausal women with secondary osteoporosis due to primary hyperparathyroidism who have refused surgery. Participants will be randomized in two groups and treated either with zoledronic acid 5 mg iv once a year or with denosumab 60 mg sc every 6 months. Investigators will compare the effect of both drugs on bone turnover markers and basic laboratory parameters after 3, 12 and 24 months of treatment, and on the bone mineral density after 12 and 24 months of treatment. All participants will take cholecalciferol 800 - 1000 IU daily.

Inclusion Criteria:

• Postmenopausal women (>12 months after last menstrual period) with primary hyperparathyroidism and with osteoporosis on Dual Energy Xray Absorptiometry (DXA) (according to International Society for Clinical Densitometry (ISCD) - criteria) and/or osteoporotic fracture of the vertebra or hip

Exclusion Criteria:

• The patient is not able to give informed consent
• other classic complications of primary hyperparathyroidism (e.g. kidney stones, renal insufficiency)
• serum albumin-corrected calcium level > 2.85 mmol/L (except when the patient is reluctant to undergo surgical treatment)
• osteoporosis treatment less than a year ago, less than two years ago in the case of oral bisphosphonate, less than three years ago in the case of parenteral bisphosphonate
• bilateral hip endoprosthesis
• additional causes for secondary osteoporosis (other than vitamin D deficiency) and pathological laboratory findings that are incompatible with the Summary of Product Characteristics (SmPC) of both medicines
• cancer, except if in stable remission of more than 5 years

Postmenopausal women

Bone mineral density, bone turnover markers and basic laboratory results will be shared.

The data will become available in 3 years. They will be available for 5 years.